Experimental Test and Performance Analysis on the Asymmetrical Operation of a Two-Section Three-Phase Coaxial HTS Cable in Chinese 10 kV Test Substation

The three-phase coaxial high temperature superconducting (HTS) cable is a promising technology for distribution network expansion in urban center. However, the three-phase coaxial structure of the superconducting cable leads to the asymmetry of the three-phase impedance parameters, which easily cause the unbalanced current in the three-phase conductors and lead to an asymmetric operation problem. A novel two-section three-phase coaxial HTS cable is proposed firstly in China Electric Power Research Institute (CEPRI) with the phase C and shield superconducting layers are divided into two sections, each with a different winding direction, pitch and HTS tape wrapping number, so they have great technical advantages in symmetrical operating performance. For validating, A 5 m, 10 kV/1 kA two-section three-phase coaxial HTS cable is manufactured as well and this HTS cable system is supercooled by LN2 closed loop cooling system with operation temperature of 73 K. The onsite high voltage test platform is set up at a 10 kV substation in Nanjing, China. The current-carrying performances of three-phase and shield layers have been experimental tested in a 10 kV transmission line. The experimental three-phase current asymmetry rate is only 4.1% which is very close to the theoretical value of 1.64%. The comparisons verify the proposed two-section structure and provide an important basis for the practical application of this kind of HTS cable in the distribution power grid.